With such kind of cards, it is required that various kinds of informations such as data concerning individual person, data concerning a company from which the cards are issued or the like data are recorded therein. In the earlier age, these informations are recorded in the form of visual characters or symbols. In the later age, they are recorded in the form of electrical signals using a magnetism. With the conventional recording means as mentioned above, it is required to take adequate measures for preventing them from being falsified or altered as well as for an increased quantity of informations.
To meet the requirement, an optical recording card to which a laser technology is applied has been developed lately. This optical recording card is such that it includes an information recording medium (optical recording medium) in which an optical reflective surface is involved. The optical reflective surface has a number of data pits formed thereon of which optical reflectivity is defferent from each other so that they are detected using a laser light on the basis of their differential reflectivity so as to allow informations in the optical recording card to be read therefrom.
The optical recording medium requires a data pit pattern for expressing data, a plurality of track guide grooves for tracking at the time of writing and reading data and a preformatting pattern indicative of addresses by which positions assumed by each sector on each track, status of usage or the like factor are represented. These preformatting pattern and data pit pattern are formed in such a fashion that data can be previously written in the optical recording medium but they can not be erased therefrom by any means.
One of methods of reading data in the optical recording medium is practiced in such a manner that a comparison is made among reflected lights with respect to their intensity. Further, one of methods of producing optical recording mediums suitable for the foregoing method is such that by employing the photographic etching technique a preformatting pattern and a data pit pattern are worked in a mask in the form of a pattern comprising a reflective metal layer so as to allow a intensity of reflectivity to be varied from position to position. In practice, a working mask is prepared when a number of optical recording mediums are produced in accordance with a contact printing process or the like method on the factory base using a master mask including a preformatting pattern and a data pit pattern. Now, to facilitate understanding of the present invention, a series of steps of producing a conventional photomask employable for producing the foregoing masks will be described below with reference to FIG. 6.
In detail, a negative is produced using an art work 112 on the basis of a specification 111 having a number of items on the optical recording medium described thereon and the thus produced negative is contracted by a contractive camera 113 so that an emulsion type or hard type reticle (intermediate mask) 114 is produced.
Then, the number of negatives is increased while the reticle (intermediate mask) 114 is contracted to an extent of 1/10 or 1/5 of the orginal figure having sizes 10 to 5 times as large as the negative scribed on the reticle (intermediate mask) 114 by operating a photorepeater 115 so that a master mask 120 is produced. A working mask 116 is obtained by printing the master mask 120.
Alternatively, a magnetic tape 118 is produced by inputting data thereinto with the aid of CAD as represented by reference numeral 117. Then, while the magnetic tape 118 is used as an inputting medium, a reticle 114 is produced by allowing the preformatting pattern to be automatically exposed to a light beam on the high resolution plate (HRP) using a pattern generator 121. Thereafter, a working mask 116 is obtained by way of the steps as mentioned above.
Otherwise, while the magnetic tape 118 is used as an inputting medium, a master mask 115 is produced using an electron beam exposing apparatus 122 so that a working mask 116 is produced also by way of the steps as mentioned above.